Distillation of water-immiscible solvents from proteinaceous residues



April 4, 1950 H. F. SAUNDERS ETAL DISTILLATION 0F WATER-IMMISCIBLE SOLVENTS FROM PROTEINACEOUS RESIDUES Filed Sept. 22, 1947 50L VENT- WE TTED ($01. VENT vAPaRs) sETTL ma TANK SOLVENT RECYCLE T0 EXTRACTION DESOL VENT/ZING VE$SEL (MIXTURE) EXTRHC TOR RESIDUES FROM AQUEOUS 'f:

ALKALINE SOLUTION (RECYCLE MIXTURE) AouEous Lina/D6 WATER WETTED RESIDUES o FURTHER TREATMENT sEPARA TOR AQUEOUS LIQUID WATER-WE TTED RESIDUES INVENTORS Patented Apr. 4, i950 WATER IMIHISCIBLE SOLVENTS FROM PROTEINACEOUS RES- DISTILLATION OF IDUES Harold F. Saunders, Shaker Heights, and Harold F. Larson, Cleveland, Ohio, assignors to The Sherwin-Williams 00., Cleveland, Ohio, acorporation of Ohio Application September 22, 1947, Serial No. 775,500

11 Claims. 1 This invention relates to improved methods for removing solvent from solvent-wetted vegetable residues, such as those remaining after solvent extraction of oils and fatty materials from oilcontaining vegetable materials, and for the production of proteinaceous materials derived from such solvent-wetted residues.

The oil-containing vegetable materials may be seeds, beans, nuts and leaves containing proteinaceous material and oil, such as cottonseed, castor beans, soya beans, peanuts, flaxseed, hempseed, sunflower seed, oiticia nut, tungnut, coconut, carnauba leaves, and the like.

Processes for extracting oils from vegetable materials with volatile organic solvents leave insoluble solvent-wetted'residues. These residues comprise cellular material, proteins, carbohydrates such as sugars, mucilages, and a small proportion of water, in more or less finely divided particles which may range in size from those of colloidal dimensions to a quarter inch or more. If the cortex or shell was not initially removed, it will also be present in the residue.

Heretofore, recovery of solvent from'the residues for reuse in the extraction step has been effected by directly heating the solvent-wetted residues alone to volatilize the solvent. The solvents with which the residues are wetted are oil-miscible organic liquids or mixtures thereof. Such solvents normally have boiling points under standard conditions of from about 35 C. to about 100 C., and when in admixture with water'under a partial vacuum, will vaporize at temperatures below about 60 C. Examples of such solvents are aliphatic hydrocarbons such as hexane and heptane and their isomers, and halogenated derivatives thereof, aromatic hydrocarbons such as benzene and mixtures of such compounds. To obtain the advantages of the present process the solvent must have a boiling point, at subatmospheric pressure, lower than the boiling point of water at the same subatmospheric pressure. Although the solvents usually have boiling points considerably below 100 C., it was generally necessary to employ temperatures above about 120 C. in order to achieve rapid and complete removal of the solvent from the residues.

The use of such high temperatures often results in charring or degradation of the residues including the proteinaceous materials, particularly when water is present in the residues as it usually is. These adverse effects often make it difiicult orimpossible to disperse the, proteinaceous materials in 'acidic, salt or alkaline solutions as is often desirable to form suspensions or emulsions useful in paints, coating materials, adhesives, etc. The practices heretofore employed in changing the solvent-wetted residues into water-wetted products have involved an intermediate drying operation which-reduces their dispersibility or solubility in water.

It is an object of the present invention to provide methods for removing solvent from solventwetted vegetable residues without using high temperaturesor prolonged heating periods which are normally required for removing solvent from the residues by direct heating.

It is a further object of this invention to transform the solvent-wetted residue to a water-wetted product without passingthe material through an intermediate dry stage, so that the dispersibility or solubility of the product is unimpaired.

It is a further object of this invention to provide a continuous method of solvent removal and/or recovery, wherein solvent-wetted residues are continuously subjected to conditions which cause vaporization of solvent. v

According to the present invention, a mixture of an aqueous liquid and a solvent-wetted vegetable residue is continuously introduced into a desolventizing zone in which a mass of such mixture is maintained under conditions which cause evaporation of the solvent. A mixture of aqueous liquid, residues which still contain solvent, and

water-wet, solvent-free residues is withdrawnfrom the desolventizing zone. The solvent-free residues are separated from the solvent-wet residues by virtue of the diflferences in wetting and/or floating characteristics of the residues caused by the removal of the solvent from some of the residues. The solvent-wet residues are recycled to the desolventizing zone for further treatment. The water-wet, solvent-free residues and aqueous liquid associated therewith are withdrawn from" the system. In order to maintain continuous and eflicient operation, the amount of original mixture of solvent-wetted residues and aqueous liquid in troduced to the system should be substantially equal to the amount of water-wet, solvent-free residues and aqueous liquid which are withdrawn from the system. a

The withdrawn water-wet residues may be used as such or may be further treated as described, for example, in the copending application Serial No. 773,481 of Harold F. Saunders.

The use of an aqueous liquid with the solventwetted residues provides several important advantages for removal of the solvent. The liquid causes greater dispersion of the residues and, hence, permits more ready vaporization of the aqueous liquid even if it is water, a neutral salt solution or an acidic solution, exceptional advantages along these lin'es are provided if the aqueous liquid is alkaline. Such a liquid inhibits, to a large extent, the coagulation of heat-coagulable proteinaceous material during the solvent removal step.

The aqueous liquid maybe mixed with the solvent-wetted residues by merely adding the water or solution directly while stirring or by adding water first and then the salt or acid or alkaline material, eitherin a dry state or in the form of a concentrated solution until the desired .pH is obtained. Generally sufiicient water is added to make an easily fiowable slurry. When the residue contains a considerable quantity of mucilages, as in the case of fiaxseed residues, more water is necessary than when a smaller quantity of mudlages is present as with soya bean, peanut and cottonseed residues.

The quantity and nature of the aqueous liquid and the particular pH values of the mixture is determined largely by the type of final products desired and the type of after-treatment to be given the water-wetted residues. These factors are fully described in the above-mentioned application of Harold F. Saunders, Serial No. 773,481.

In the mixture containing the aqueous liquid, solvent, and solvent-wetted residues, the solids are preferentially wetted by the solvent, and tend to float with the solvent on the aqueous liquid. In this state, the mixture is filterable only with difficulty, if at all, and resists separation by centrifuging, since the solids tend to flow off with the liquid. As the solvent is removed, the solids in the mixture become preferentially wetted by water and begin to settle in the aqueous liquid. After this change in wetting of the solids occurs, they can be readily separated from the mixture by filtration, settling or centrifuging.

According to the present method the mixture of solvent-wetted residues and the aqueous liquid is subjected to mild heat under a partial vacuum,

preferably while its surface is being agitated and splashed to enlarge the surface and thereby facilitate evaporation of solvent therefrom. This may be accomplished in various ways, as by continuously introducing the mixture into the top of a vessel and letting it fall or spraying it onto an accumulation of the mixture in the bottom of the vessel. The surface of the mixture may also be enlarged by flowing the mixture over bailies. If desired, a stirrer may be provided in the bottom of the vessel to keep the accumulated mixture agitated sufllciently to prevent excessive setting of solid material. The evaporation of solvent is carried out at a subatmospheric pressure of about 28 inches and at a temperature between the boiling points of the solvent and water at the pressure employed. The mixture is then withdrawn from the vessel and a portion recycled to the top of the vessel. The remaining portion of the partially desolventized mixture is passed to a separator such as a settling tank or the like. As stated above, during the removal of the solvent, at least a portion of the residue becomes wetted with water and will settle in the aqueous liquid while that portion of the residue which remains wetted with solvent willfioat upon the aqueousliquid. Therefore, when themixture has been subjected to the conditions for solvent removal and a portion thereof transferred to a separator, the solvent-free, water-wetted residue is easily separable from the remaining solventwetted residue which can be recycled to the desolventizing vessel for further treatment with additional fresh mixture and with the unseparated portion of the mixture.

With reference to the drawing, which is a diagrammatic flow sheet of a system for carrying out the present invention, the solvent-wetted residues from an oil extraction operation are introduced through line H to a mixer I2 where the residues are, rapidly stirred while an aqueous liquid is introduced through line I3 and mixed therewith. If desired, water may be introduced throughline l3 and a concentrated alkaline solution may be added through line l3a. When the resulting mixture has the desired pH, it is passed continuously through line M to the top of a I vessel will be maintained.

As illustrated in the drawing, the mixture which is introduced through line H is sprayed onto a pool of the mixture which is provided in the bottom of the vessel IS. The solvent vapors which are liberated in the vessel l5 are withdrawn through line l6. Line i6 is connected to a vacuum pump (not shown) so that the vessel l5'is maintained at a sub-atmospheric pressure of about 28 inches. The solvent vapors which are withdrawn through line l6 can be condensed, separated from any water present and recycled to the oil extraction stage.

A substantial proportion of solvent will be removed from the mixture in the desolventizing vessel l5 and consequently a large quantity of the solvent-wetted residues will become waterwetted. A portion of this mixture is then recycled from the bottom of the vessel l5 through a line I! to line It and reintroduced into vessel l5 along with additional fresh mixture. The remaining portion of the mixture is passed through line l8 to a settling tank l9 where it is permitted to stratify.

That portion of partially desolventized mixture from vessel l5 which is recycled through line ll to line [4 may vary from about 10% to about 95% of the mixture withdrawn from the vessel depending on various conditions. For example, it is desired to effect a high degree of splashing in the vessel 15 in order to more efliciently evaporate the solvent. This requires a relatively large volume of mixture as well as rapid flow through the vessel. If only freshly prepared mixture were introduced in large volume, the degree of desolventizing would be low since the mixture would be subjected to the splashing action for only a short period of time. It is therefore generally desirable to recycle from about 50% to about 90% of the partially desolventized mixture to the top of the vessel l5.

0n the other hand, when a very low pressure is maintained and separate means for agitating the mixture are provided in the vessel, it is sometimes possible to obtain satisfactory desolventizetion even when only about 10% of the partially moans desolventized mixture is recycled through lines :1 and u. In the settling tank I! will comprise the remaining solvent-wetted resithe remaining portion 2 of mixture stratifies and the lighter or upper layer due and'some of the aqueous liquid and is withdrawn through line and recycled to the top of thevessel l5 for further evaporation of solvent. The lower layer which comprises aqueous liquid and the water-wetted residue is withdrawn through line 2|. This material may be further treatedin accordance with'the process described additional treatment if desired, asmentioned in the aforesaid application Serial No. 773,481, while the solids, which are still moist with aqueous liquid, can be withdrawn through line for use as such. v r i The settling tank I9 may, if desired, be maintained at subatmospheric pressure as is the desolventizing vessel 15. This may be accomplished by means of line 26 which connects the settling tank [9 with line l6. Under these circumstances any solvent vapors which are liberated in the settling tank may be returned to the solvent vapor line It for subsequent condensation and reuse.

Various conventional elements omitted from the drawings for the sake of simplicity, but it would be obvious to one skilled in the art that various valves, metering devices, temperature control and indication devices, pressure indicators, pH indicators, pumps, and the like can be used without departing from the spirit of the present invention.

According to the present invention, a vegetable residue wetted with an organic solvent, for example a residue from a heptane oil-extraction operation, is mixed in mixer-l2 with water and a concentrated alkaline solution such as caustic soda, potash, ammonium hydroxide or the like, until a pH value of from about 8 to about 11 is attained. This pH value afiords substantially This mixture'is then passed through line M.

to vessel l5 which is maintained at a temperature of from about C. to about C. and at a subatmospheric pressure of about 28 inches. As the mixture falls to the bottom of the vessel IS, a substantial quantity of the heptane is evaporated and withdrawn through line I6.

A portion of the mixture is recycled to vessel while the remaining mixture is passed to settling tank IQ for separation of the aqueous phase containing the water-wetted residues from the phase containing the heptane-wetted residues and some of the aqueous liquid. The lastmentioned phase is recycled through line 20 to the vessel l5 for further evaporation of heptane along with additional fresh mixture and the rehave been cycled portion mentioned above. The lower, or aqueous phase, is withdrawn through line 2| and may be used as such or may be treated further in accordance with the process described in application Serial No. 773,481. On the other hand, the aqueous phase may be further separated in the separator 23 to obtain a moist solid material and an aqueous liquid substantially free of solids. The liquid can be further treated while the solids may be used as such.

What is claimed is:

1. A continuous method for treating vegetable residues wetted with a substantially water-insoluble organic: solvent having a lower boiling point than that of water under the same subatmospheric pressure, comprising mixing said residues with an aqueous liquid, continuously providing said mixture with a large surface area,

oration of solvent therefrom.

maintaining said mixture, while under subatmospheric pressure, at a temperature between the boiling points of the solvent and water at the pressure. employed to evaporate at leasta portion of said solvent, and separating at least a portion of said mixture into an aqueous liquid phase containing water-wetted residues and a phase containing solvent-wetted residues.

2. A method as claimed in claim 1 wherein the vegetable residues are derived from the solvent extraction of oil from comminuted oil bearing vegetable materials. I

3. A method as claimed in claim 1 wherein a portion of the partially desolventized mixture is recycled to the evaporating step for further evap- 4. A method as claimed in claim 1 wherein the aqueous liquid is an aqueous alkaline solution;

5. A method as claimed in claim 1 wherein the mixture is sprayed to provide the large surface area.

6. A method as claimed in claim 1 wherein the separation of the mixture is carried out at subatmospheric pressure for further evaporation of solvent.

7. A method as claimed in claim 1 and further comprising removing the water-wetted residues from the separated aqueous phase.

8. A continuous method for treating vegetable residues wetted with a substantially water in:- soluble organic solvent having a lower boiling point than that of water under the same subatmospheric pressure, comprising mixing said residues with an aqueous liquid, heating said mixture to a temperature not higher than about C. while under subatmospheric pressure to evaporation at least a portion of said solvent, recycling a portion of said partially desolventized mixture to the'evaporation step for further evaporation of solvent, collecting the remaining portion of the at least partially desolventized mixture, separating said collected mixture into an aqueous phase containing waterwetted residues and a phase containing solventwetted residues and some aqueous liquid, recycling said last mentioned phase to the evapora-' tion step for. further removal of solvent and withdrawing said aqueous phase.

9. A continuous method for treating vegetable residues wetted with a substantially water-insoluble organic solvent having alower boiling point than that of water underthe same subatmospheric pressure, comprising mixing said residues with an aqueous liquid, directing said mixture onto a pool of accumulated mixture while being maintained at a temperature not higher than about 60 C. and at subatmospheric pressure to evaporate at least a portion of said solvent, recycling a portion of said partially desolventized mixture to the evaporation step for further evaporation of solvent, collecting the remaining portion of the at least partially desolventized mixture, separating said collected mixture into an aqueous phase containing waterwetted residues and a phase containing solventwetted residues and some aqueous liquid, recycling said last mentioned phase to the evaporatiOn step for further removal of solvent and withdrawing said aqueous phase.

10. A method as claimed in claim 9 and further comprising treating the aqueous phase to separate an aqueous liquid from the solids.

11. A continuous method for treating vegetable residues wetted with a substantially water insoluble organic solvent having a lower boiling point than that of water under the same subatmospheric pressure, comprising mixing said residues with an aqueous alkaline solution, spraying said mixture into the top of a desolventizing vessel maintained at a temperature not higher than 60 C. and at a subatmospheric pressure of about 28 inches, splashing said sprayed mixture onto a pool of accumulated mixture at the bottom of said vessel, withdrawing solvent vapors from said vessel, withdrawing a mixture 01' alkaline solution, water-wetted residues and solventwetted residues from the bottom of said vessel, recycling a portion of said last mentioned mixture to said spraying step, introducing the remainder of said last mentioned mixture into a REFERENCES CITED The following references are of record in the file 01' this patent:

UNITED STATES PATENTS Number Name Date 2,315,422 Hildebrandt Mar. 30, 1943 2,395,901 Murphree Mar. 5, 1946 2,396,600 Pacevitz Mar. 12, 1946 2,406,648 Weisberg Aug. 27, 1946 2,417,131 Schmitt Mar. 11, 1947 

1. A CONTINUOUS METHOD FOR TREATING VEGETABLE RESIDUES WETTED WITH A SUBSTANTIALLY WATER-INSOLUBLE ORGANIC SOLVENT HAVING A LOWER BOILING POINT THAN THAT OF WATER UNDER THE SAME SUBATMOSPHERIC PRESSURE, COMPRISING MIXING SAID RESIDUES WITH AN AQUEOUS LIQUID, CONTINUOUSLY PROVIDING SAID MIXTURE WITH A LARGE SURFACE AREA, MAINTAINING SAID MIXTURE, WHILE UNDER SUBATMOSPHERIC PRESSURE, AT A TEMPERATURE BETWEEN THE BOILING POINTS OF THE SOLVENTS AND WATER AT THE PRESSURE EMPLOYED TO EVAPORATE AT LEAST A PORTION OF SAID SOLVENT, AND SEPARATING AT LEAST A PORTION OF SAID MIXTURE INTO AN AQUEOUS LIQUID PHASE CONTAINING WATER-WETTED RESIDUES AND A PHASE CONTAINING SOLVENT-WETTED RESIDUES. 